1. Field of the Invention
This invention relates to the preparation of copolyamides and is particularly concerned with amorphous lactam-imidazoline derived copolyamides.
2. Description of the Prior Art
Various types of polyamide polymers are known; see for example The Encyclopedia of Polymer Science and Technology, Vol. 10, p 347 et seq, 1969, Interscience Publishers, New York, N.Y. The various kinds of repeating units disclosed therein which are linked by the carbonamide group ##STR1## determine the variation in physical properties observed for the different types of polyamides. Physical properties like melting point, solubility, and crystalline state are almost solely dependent on the type of repeating unit employed. For example, when all the repeating units are aromatic the polyamide has such a high melting point that melt processability, such as injection molding, is precluded because polymer decomposition begins to occur before the melt stage is ever reached.
Alternatively, when the repeating units are mixed aliphatic-aromatic, as in the case of a polyamide prepared from an aliphatic dicarboxylic acid and an aromatic diamine, the polymer is injection-moldable but because of high crystallinity is brittle, opaque, and possessed of low elongation. In fact, when the dicarboxylic acid component is either adipic, pimelic or suberic acid, the corresponding polyamides have decomposition temperatures below their melting points. This behaviour precludes melt processing these polymers; see J. Polymer Sci. 10, Part A-1, p 1547, 1972. Finally, when the repeating units are all aliphatic as in nylon-6,6 or nylon-6 (polycaprolactam), the polymer is injection moldable but is limited in the end-use temperature to which it can be exposed.
T. Kagiya et al reported the formation of crystalline polyamides from bisimidazolines and dicarboxylic acids [Journal of Polymer Science: Part A-1, Vol. 5, pp 1129-1135 (1967)]. An advantageous feature of the polyamides prepared thereby was the avoidance of a dehydration step which is necessary when similarly constituted polyamides are prepared via the diamine-dicarboxylic acid route. This means of obtaining copolyamides was elaborated and expanded upon by Fuki et al., Japanese Application No. 44-29265, Nov. 28, 1969.
Further disclosures of the use of bisimidazolines in the formation of crystalline polyamides are to be found in Japanese Applications Nos. 44-29466 and 44-29467 (both published Dec. 1, 1969). In the former application bisimidazolines and bisdicarboxylic acid imides are copolymerized with water or a nylon salt (combination of a diamine and dicarboxylic acid in 1:1 molar proportions). In the latter application the bisimidazolines are co-reacted with bisdicarboxylic acid imides and amino-carboxylic acids.
Lactam polymerizations, an particularly the use of .epsilon.-caprolactam to prepare the nylon-6 type of polyamide, are very well known. Further, the use of caprolactam in the formation of caprolactam copolyamides is well known in the art. For example, for various combinations of caprolactam with aliphatic and aromatic dicarboxylic acids and diamines see U.S. Pat. Nos. 3,850,887; 3,926,924; 3,933,762; 4,024,116; 4,102,871; 4,118,351 and 4,196,108.
We have now discovered a novel class of amorphous copolyamides which are based on certain bisimidazolines, dicarboxylic acids, and lactams.
The present copolyamides are possessed of heat resistant properties falling between those of the caprolactam based nylon-6 type materials and the highly aromatic copolyamides of the type disclosed in U.S. Pat. Nos. 4,072,665 and 4,087,481. Because the present copolymers have greater heat resistance than the caprolactam based materials yet are more easily molded, extruded, etc., than the highly aromatic based materials, they provide a highly useful addition to the known polyamides.
It has been found that a certain type of arylene linkage (namely 1,3-arylene) must be present within certain minimum proportions to achieve both the amorphous character and high temperature resistance of the polymers in accordance with this invention. The replacement of the 1,3-arylene linkage by the 1,4-arylene linkage results in the formation of crystalline polymers which are not within the scope of the present invention.
Additionally, the preparation of the present copolyamides is accomplished in an energy efficient process because no complicated operation, such as a dehydration or catalyst removal step, is required. In this same connection, the present polymers are easily prepared without the evolution of troublesome by-products.